Effects of [Zn0.5Si0.5]3+ Substitution on Microwave Dielectric Properties of ZnAl2-x(Zn0.5Si0.5)xO4 Ceramics

Microwave dielectric ceramics are indispensable in modern communication technologies, playing a pivotal role in components such as filters, oscillators, and antennas. Among these materials, ZnAl2O4 ceramics have garnered attention for their excellent quality factor (Q × f) and low dielectric constant (εr). However, their high sintering temperature (~1650 °C) limits practical applications. This study investigates ZnAl2-x(Zn0.5Si0.5)xO4 (ZAZS) (x = 0.1–0.9) ceramics, where [Zn0.5Si0.5]3+ substitutes Al3+, to reduce sintering temperature while maintaining high-performance microwave dielectric properties. ZAZS ceramics were synthesized via the solid-state reaction method and characterized for their structural, morphological, and dielectric properties. X-ray diffraction analysis confirmed the formation of a single-phase solid solution up to x = 0.8, with minor secondary phases appearing at x = 0.9. The substitution increased lattice parameters and enhanced material densification, as observed through SEM and relative density calculations. Microwave dielectric measurements showed that ZAZS ceramics achieved a maximum Q × f of 20,200 GHz and a τf value reduced to −62 ppm/°C at x = 0.8, while εr decreased from 7.90 to 6.98. Bond-valence calculations reveal that the reduction of the average Al/Zn/Si–O bond valence weakens octahedral rigidity, systematically tuning τf toward zero. These results demonstrate that ZAZS ceramics, with a reduced sintering temperature of 1400 °C, exhibit excellent potential for application in low-loss microwave devices.